Hermetically sealed switch with tubular dielectric portions united to a relatively larger metallic intermediate vapor condensing portion



1965 L. o. JACOBS 3, 3 ,704 HERMETICALLY SEALED SWITCH WITH TUBULARDIELECTRIC PORTIONS UNITED TO A RELATIVELY LARGER METALLIC INTERMEDIATEVAPOR CONDENSING PORTION Filed April 9, 1963 INVENTOR. 4 LESTER O.JACOBS United States Patent Y 3,231,704 HERMETICALLY SEALED SWITCH WITHTUBU- LAR DIELECTRIC PORTIONS UNITED TO A RELATIVELY LARGER METALLICINTERME- DIATE VAPOR CONDENSING PORTION Lester 0. Jacobs, San Jose,Calif., assignor to Jennings Radio Manufacturing Corporation, San Jose,Calif., a corporation of Delaware Filed Apr. 9, 1963, Ser. No. 271,696 5Claims. (Cl. 200144) This invention relates to switches and moreparticularly to high power switches of the hermetically sealed andvacuum types for interrupting electrical currents of large magnitude.

One of the limiting factors in conventional power switches is theconstruction of the envelope, which may be designed to withstand aninternal pressure, as where the envelope is gas filled, or which may bedesigned to withstand atmospheric pressure, as where the envelope isevacuated. In either case, it has been found that Where the envelope isfabricated in part from glass and in part from metal that the union ofthe glass to metal. portions of the envelope constitute weak points inthe construction, and prevent outgassing of the envelope parts atelevated temperatures. Accordingly, it is one .of the objects of theinvention to provide a hermetically sealed switch incorporating anenvelope fabricated from materials which may be flexibly united andoutgassed at a considerably higher temperature than when glass is used.

In the fabrication of glass and metal switch envelopes it has beencommon practice to use the well known Houskeeper seal in which a thinlyfeathered metallic flange is embedded in the glass, the theory beingthat if the metal is thin and sufliciently ductile it be dominated bythe glass. Because this construction is inherently weak, attempts havebeen made to substitute a metallic member having a coefficient ofthermal expansion and contraction more closely approximating that ofglass, as for instance Kovar, and casting glass about an unfeatheredflange. While this construction is an improvement over the conventionalHouskeeper seal, it still imposes problems such as reduced electricalconductivity of the metal portions and destructive thermal shock to theglass if removed from the casting mold before it has cooledsufficiently, thus increasing .the elapsed time required to fabricate aswitch. Accordingly, another object of the invention is the provision.of an envelope construction in which glass is eliminated and inwhichceramis and metal are associated in a manner to provide a strongyet flexible hermetic union between the partswhich will accommodatedifferences in the thermal expansion and contraction characteristics ofthe dissimilar material.

Another problem .that has defied solution has been containment toprescribe-d areas within the envelope of metal particles and vaporizedcontact metal sputtered from the switch contacts upon the striking of anare.

In switches utilizing a thin flexible bellow high velocity metallicparticles often puncture the bellow, thus destroying the envelope. Thesame problem exists with Houskeeper seals in which the thinly featheredmetal-lie flange may be punctured by fast moving metallic particlesblown from the contacts. To meet this problem shield structures ofvarious designs have been utilized to shield both the bellow and theHouskeeper seals. These shield structures are diflicult to fabricate,are not complete'ly effective and increase the cost of each unit,therefore making it less available for applications where cost is animportant factor. Accordingly, still further object of the invention isthe provision of aswitch envelope fabricated from ceramic and metal, andwhich incorporates an intermediate heavy metallic toroidal shell portioneasily fabricated, and preferably arranged, with re 3,231,794 PatentedJan. 25, 1966 spect to the switch contacts, so as to intercept andcondense a large portion of the metal particles and vapor emanating fromthe switch contacts.

Manufacturers of high power switches have also been plagued by thetendency of vaporized contact metal to condense on the inner surface ofdielectric members Whose function it is to electrically insulate spacedmetallic members. Shields of this type are often mounted directly oncurrent carrying elements of the switch, and are therefore maintained ata temperature sufliciently high as to be detrimental to their normalfunction of condensing vaporized contact metal. It is therefore stillanother object of the present invention to provide shielding for theceramic components of the switch envelope such that heat in the shieldstructure is conducted out of the envelope to thus increase theeffectiveness of the shields.

Shields of this character have in the past been secured as by brazing toassociated structure, which procedure complicates assembly andfabrication of the switch and increases the cost thereof. It istherefore a still further object of the invention to provide ahermetically sealed power switch incorporating shield structurestherewithin secured in their position by associated structure withoutthe need of brazing, thus facilitating fabrication of the switch.

Another problem that has become apparent from the use of shields in theimmediate area surrounding the contacts of a power switch has beenconfinement of ionized vapor surrounding the switch contacts and thuspreventing rapid extinguishing of an arc. It is therefore another objectof the present invention to provide an envelope in which the condensingsurfaces for vaporized material are spaced relatively far away from thecontacts which they surround.

The invention possesses other objects and features of advantage, some ofwhich, with the foregoing, will be apparent from the followingdescription and the drawing. It is to be understood however that theinvention is not limited by the said description and the drawing but maybe embodied in various forms within the scope of the appended claims.

Broadly considered, the power switch of the invention comprises anhermetically sealed envelope including a pair of elongated axiallyaligned and spaced tubular dielectric members, preferably of ceramic,held apart and hermetically united to an intermediate heavy metallictoroidal envelope section by flexible ceramic-to-metal unions. Eachopposite end of the composite structure so formed is closed by ametallic end cap structure hermetically united to the associated end ofthe tubular ceramic member by flexible ceramic-to-metal unions. Mountedon each end cap structure and extending into the envelope coax'iallywith respect to the tubular ceramic members is a conductive metallicstem having a contact member fixed of its inner free end lying withinthe confines of the intermediate toroidal envelope member. To providefor axial displacement of one of the two opposing contacts, one of thestems is slidably arranged with respect to its associated end capstructure and the slidable union is appropriately sealed as by aflexible metallic bellow hermetically interposed between the stem andend cap structure. Thus, opening of the switch contacts under load,which usually causes arcing between the contacts, will result in :theevaporation of contact metal, but such vaporized metal will be condensedon the inner surface of the intermediate toriodal section of theenvelope. Because there is the possibility that some of the vaporizedcontact metal will deposit itself on the inner surfaces of the tubularceramic members unless prevented, appropriate shields are providedinterposed between the contacts and the associated tubular ceramicmembers. As illustrated in the drawing, each shield is trapped betweenthe associated ceramic member and a peripheral edge" portion of the'intermediate toroidal envelope section without the need for brazing.

Referring to the drawings:

The figure is a vertical sectional view partly in elevation showing thedetails of construction of the switch. The figure is drawn approximatelyactual size.

In more specific terms, the power switch of the invention comprises anhermetically sealed envelope including elongated tubular dielectricportions 2 and 3, preferably fabricated from ceramic, axially alignedand spaced apart by an intermediate metallic toroidal envelope section4, having a pair of peripheral edge portions 6 and 7, the peripheraledge portion 6 being hermetically united to the associated end of thetubular ceramic 2 by a thin flexible annular metallic sealing structure8. As illustrated, the sealing structure includes a radially inwardlyextending flange 9 brazed to the metalized end of the tubular ceramic,and a cylindrical flange 12 brazed to the peripheral edge portions 6-7of the intermediate toroidal envelope section. The hermetic unionbetween flange 9 and the associated tubular ceramic 2 or 3 isstrengthened by a dielectric back-up member or ring 13 brazed to theassociated flange 9 but free to slide on the supporting peripheral edgeportion of the intermediate envelope section, or on an intermediatestructure interposed between the back-up ring and each portion 6 or 7.Thus, diflerences in thermal expansion and contraction between the partsis accommodated by the slidability of the ceramic back-up ring 13 on theadjacent metallic structure, while the sandwiched flange 9 is dominatedby the ceramics between which it is brazed.

The ends of the tubular ceramic envelope portions 2 and 3 remote fromthe intermediate metallic envelope section 4 are closed by end capstructures 14 and 16, respectively. The end cap structure 14 comprisesan annular flat metallic plate section 17, and an integral tubularcentral section 18. The outer peripheral edge portion of the annularplate portion 17 is hermetically united to the associated end of ceramic2 by a flexible metallic sealing structure 8 similar to that previouslydescribed and functioning in the same manner. This union also utilizes aback-up ring 13 brazed on the one hand to the sealing structure 8 andslidably abutting plate member 17 to accommodate differences in thermalexpansion and contrac tion between the dissimilar parts.

Supported within the central tubular portion 18 of end cap 14 is aconductive metallic stem 19 extending coaxially into the envelope andprovided on its inner free end with an integral contact button 21 havinga contact surface 22 lying in a median plane between peripheral edgeportions 6 and 7 of the intermediate metallic envelope section 4.

The end cap structure 16 is somewhat diflerent from the end capstructure 14 in that a separate flexible sealing structure 8 is not usedto unite this end cap to the associated end of ceramic 3. Instead, theend cap 16 is provided with an integral flexible metallic radiallyoutwardly extending flange 23 hermetically brazed between the metalizedend of ceramic 3 and ceramic back-up ring 24. The flange 23 mergesimmediately Within the inner periphery of the ceramic 3 with a thincylindrical flange exten sion 26 concentrically arranged with respect todielectric members 23 and 24. The change of direction of the flange atthis point is important in that it takes out'of the plane of the unionbetween flange 23 and the associated ceramics the mass of materialmaking up the remainder of the end cap structure so that differences inthermal expansion and contraction of this larger mass is accommodated'byflexure of the lever arm formed by cylindrical flange 26 while theflange 23 is dominated by the ceramics. The end cap structure 16 iscompleted by annular plate portions 27 and 28 joined by cylindricalflange 29, and a tubular centrally disposed flange 31.

Br-azed within the cylindrical flange 31 is the outer open-end 32 of aflexible metallic bellow 33, the inner end 34 of which is hermeticallybrazed to an intermediate section of a cylindrical conductive stem 36,slidably supported on the end cap structure 16 within the central flange31', and which extends into the bellow as shown. A relatively largerdiameter stem extension 38 integral with the stem 36 is provided with acontact button 39 having contact surface 41 adapted to make and breakcontact with contact surface 22 of the opposing contact button. Toactuate the movable contact assembly formed by stem 36, stem extension38, and contact button 39, the end of the stem 36 is provided with atapped hole 42 for engagement by any suitable actuating means such as asolenoid.

To shield the inner surface of the tubular cerami envelope portions 2and 3, respectively, shield structures 42 and 43 are provided, eachhaving cylindrical portions disposed concentrically with respect to theassociated tubular ceramic and lying between the ceramic and the contactbuttons 21 and 39. Each of the shield structures is provided with aradially outwardly extending flange 44 caught between the associatedback-up-ring 13 and the adjacent peripheral portion 6 or 7 as shown. Theflange 44 is provided with a jogged portion forming a shoulder to guidenesting of the shield structure on the peripheral edge portion ofmetallic toriodal envelope section 4. This construction facilitatesfabrication of the switch because it permits automated stacking andselfalignment of the parts, thus facilitating machine assembly andbrazing of the assembly in a single operation.

To further insure that vaporized metal is not deposited on the innersurface of the tubular dielectric envelope portion 3, or that highvelocity metallic particles do not puncture the flexible bellow 33, anauxiliary shield 47 is provided having a flat plate portion 48 caughtbetween the inner end of bellow 34 and stem extension 38, and acyclindrical portion 49 concentrically interposed in radially spacedrelation between the cylindrical shield 43 and the adjacent tubularceramic envelope portion 3. Thus, before vapor or metallic particles canreach the dielectric envelope portion they must pass through thelabyrinth formed by the shields 43 and 47. Experience has shown thatvery little metal is deposited on the inner surfaces of the ceramics inthe envelope illustrated.

I claim:

1. A switch comprising an hermetically sealed envelope including a pairof axially aligned tubular dielectric envelope portions having adjacentends spaced apart and hermetically united to an intermediate annularmetallic shell portion of the envelope relatively larger in diameterthan said aligned tubular dielectric envelope portions, end capstructures closing opposite ends of the tubular dielectric envelopeportions, axially aligned fixed and movable conductive contact stemsmounted on opposite end caps, conductive contact surfaces on the innerends of the contact stems within the intermediate annular metallic shellportion of the envelope, and a flexible bellow hermetically interposedbetween one of the end caps and the movable contact stem to accommodateaxial displacement of the movable contact stem with respect to theenvelope to make or break a circuit through the switch; said relativelylarger metallic shell portion forming condensing surfaces spacedrelatively far away from the contacts, said surfaces condensingvaporized material emanating from said contact surfaces.

2. The switch according to claim 1, in which the intermediate metallicannular shell portion comprises a pair of axially spaced innerperipheral edge portions connected by an intergal semi-cylindricalsection concave in a direction facing the contacts.

3. A switch comprising an hermetically sealed envelope including a pairof axially aligned tubular dielectric portions having adjacent endsspaced apart and an intermediate annular metallic shell portioninterposed between the spaced apart ends of the tubular dielectricportions, a seal assembly flexibly uniting hermetically one end of eachtubular dielectric portion with the intermediate annular metallic shellportion, said seal assembly including a dielectric back-up ringsupported by the intermediate annular metallic shell portion, end capstructures closing opposite ends of the tubular dielectric portions,axially aligned fixed and movable conductive contact stems mounted onopposite end caps, conductive contact surfaces on the inner ends of thecontact stems within the intermediate annular shell portion of theenvelope, a flexible bellow hermetically interposed between one of theend caps and the movable contact stem to accommodate axial displacementof the movable contact stem with respect to the envelope to make orbreak a circuit through the switch, and a shield structure within theenvelope interposed between each tubular dielectric envelope portion andthe contacts to intercept vaporized material therefrom and including amounting flange slidably caught between the back-up ring of each sealassembly and the associated peripheral edge portion of the intermediateannular metallic shell portion so as to conduct heat from the shield tothe intermediate annular metallic shell portion.

4. The switch according to claim 3, in which each shield structureincludes a tubular shell coaxially arranged in radially spaced relationwith respect to the associated tubular dielectric portion of theenvelope.

5. The switch according to claim 4, in which an auxiliary shield ismounted on the movable contact stem to shield the bellows fromdestructive metallic particles emanating from the contacts, saidauxiliary shield including a cylindrical flange portion concentricallyarranged in radially spaced relation between the adjacent tubulardielectric portion and the coaxially arranged tubular shell of theassociated shield structure.

References Cited by the Examiner UNITED STATES PATENTS 2,965,734 12/1960 Timmerman 200144 2,979,588 4/1961 Jennings 200144 3,038,980 6/1962Lee 200144 FOREIGN PATENTS 769,935 3/ 1937 Great Britain. 135,939 2/1962Russia.

KATHLEEN H. CLAFFY, Primary Examiner. ROBERT K. SCHAEFER, Examiner.

1. A SWICH COMPRISING AN HERMETICALLY SEALED ENVELOPE INCLUDING A PAIROF AXIALLY ALIGNED TUBULAR DIELECTRIC ENVELOPE PORTIONS HAVING ADJACENTENDS SPACED APART AND HERMETICALLY UNITED TO AN INTERMEDIATE ANNULARMETALLIC SHELL PORTION OF THE ENVELOPE RELATIVELY LARGER IN DIAMETERTHAN SAID ALINGED TUBULAR DIELECTRIC ENVELOPE PORTIONS, END CAPSTRUCTURES CLOSING OPPOSITE ENDS OF THE TUBULAR DIELECTRIC ENVELOPEPORTIONS, AXIALLY ALIGNED FIXED AND MOVABLE CONDUCTIVE CONTACT STEMSMOUNTED ON OPPOSITE END CAPS, CONDUCTIVE CONTACT SURFACES ON THE INNERENDS OF THE CONTACT STEMS WITH THE INTERMEDIATE ANNULAR METALLIC SHELLPORTION OF THE ENVELOPE, AND A FLEXIBLE BELLOW HERMETICALLY INTERPOSEDBETWEEN ONE OF THE END CAPS AND THE MOVABLE CONTACT BETWEEN TOACCOMODATE AXIAL DISPLACEMENT OF THE MOVABLE CONTACT STEM WITH RESPECTTO THE ENVELOPE TO MAKE OR BREAK A CIRCUIT THROUGH THE